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Thermal Mass Flow Meters

What are Thermal Flow Meters?

Thermal Flow meters are referred to in a variety of variations: thermal flow meters, thermal meters, thermal mass flow meters, calorimetric flow meters, and thermal dispersion flow meters. They all are referring to the same principle of operation.

Thermal mass flow meters operate on the principal that a flow stream produces a rate of heat transfer, where heat is removed and cooling takes place, that is proportional to the mass flow of the media. There are two elements to a typical thermal mass flowmeter, a heating element and a sensing element. The heating element is cooled by the flow and is detected by the sensing element. This difference is translated into a flow value.

To envision how this works, imagine you are standing outside in a t-shirt on a fall day. There is a light breeze blowing, it’s about 60 degrees and you are comfortable. Now imagine that the breeze turns into a strong wind. The increase in the wind speed begins to chill you because your skin is losing more heat. This is the same principle that thermal mass flow meters operate on. The stronger the wind, the less heat you retain. With thermal dispersion measurement, the more flow there is, the less able the probe is able to retain heat in the flow stream.

Thermal Mass Flow Meter Working Principle

What are Thermal Flow Sensors?

“Flow sensors” are a generic term for flow meters, flow switches, and flow indicators because they are all, in a sense, sensing (or detecting) flow.

Thermal flow sensors are primarily used for laminar-flowing gas in closed systems, although liquids can also be measured and monitored by thermal mass flow sensors.

Do Thermal Flow Meters Come in Insertion or Inline Models?

Thermal mass flow meter come in both inline and insertion models. Insertion type probes offer an easier installation process for existing systems in that it only requires a hole to be made in the pipe versus fully severing the pipe to install an inline flow meter. Insertion models also typically offer less pressure drop than inline thermal mass flow meters. They also offer a more economical option for large pipe diameters than inline meters.

For insertion type flow meters, it is important to note that flow velocity is not uniform across the pipe section and for accurate measurements, the measuring probe must be positioned correctly within the pipe circumference. The tip must be completely covered by the media and the pipe should be full and bubbles should be avoided.

Insertion probes require little to no maintenance and only need to be checked if the media is known to create deposits on the probe.

What are Thermal Dispersion Flow Switches?

Unlike some other flow meter technology types, thermal dispersion technology is available as a “stand-alone” flow switch. Many thermal mass flow meters will also offer integral or optional switching capabilities if flow rate measurement is also essential to the process.

Thermal Dispersion Flow Switches

What are the Advantages of Thermal Mass Flow Meters?

  • Compatible with many gases
  • Can be used with saturated gases
  • Accurate and repeatable over a wide range
  • No moving parts to wear or break
  • Low maintenance
  • Long operational life
  • Designed for heavy-duty industrial use
  • High flow rate sensitivity
  • High turndown ratios, up to 100:1
  • More economical than other mass flow technology types (Coriolis)
  • Unaffected by changes in pressure, temperature, and density
  • Quick reaction time to changes in the flow
  • Lower installation cost, no extra instrumentation is needed
  • Inline models and insertion models for large pipe diameters
  • Straight pipe runs can be reduced using dual plate flow conditioning

What are the Disadvantages and Limitations of Thermal Mass Flow Meters?

  • Calibration is specific to a particular gas or mixture and accuracy decreases if changed
  • Typically only for clean, non-abrasive media
  • Thermal properties of the media must be known
  • Initially the cost can be higher than other technology types

What are the Applications for Thermal Mass Gas Flow Meters?

  • Oil & Gas, Upstream and Downstream
  • Refineries
  • Petrochemicals
  • Power Plants
  • Nuclear Plants
  • Clean Energy
  • Landfill Gas Recovery, Biogas
  • Flare Gas
  • Stack or Flue Gas
  • Aeration
  • Wastewater Treatment
  • Food & Beverage
  • Mining & Metals
  • Manufacturing
  • HVAC
  • Pharmaceuticals
  • Marine Industry
  • Consumption & Supply Monitoring
  • Leak Detection
  • Monitoring Distribution Networks
  • Mixing & Blending of Gas
  • Burner or Boiler Feed Control

What Types of Gas Can be Used with Thermal Flow Meters?

  • Compressed Air
  • Carbon Dioxide
  • Argon
  • Nitrogen
  • Oxygen
  • Natural Gas
  • Biogas
  • Air

Thermal Mass Flow Meter Manufacturers

KOBOLD manufacturers and sells industry-recognized thermal mass flow meters and flow switches. We offer models for liquids and models for gas. We offer both inline and insertion models. Call us today to speak with one of our knowledgeable engineering staff about which thermal mass flow meter or switch is the best fit for your specific application.

Learn more about why you should partner with KOBOLD for your application.

Help Selecting a Thermal Flow Meter
Featured Products
Anemometer Air Flow Sensor
KAH - Air Velocity Sensor

For Gas | Low Flow Velocities | User Selectable Sensing Range | Adjustable Probe Insertion Depth | Adjustable Damping Time | Up to 4,000 ft/min | Up to 122 °F

Thermal Dispersion Flow Meter
KAL-A - Thermal Flow Sensor for Water-Based Liquids

Made in the USA | For Water-based Liquids | Insensitive to Dirt and Debris | Low Pressure Loss | Up to 6.6 ft/sec | Up to 1,450 PSI | Up to 176 °F | NPT or Tri-Clamp Threads

Compact Insertion Thermal Flow Switch
KAL-D - Compact Thermal Flow Switch for Water-Based Liquids

Made in the USA | For Liquids | Stainless Steel Build | Up to 6.6 ft/sec | Up to 580 PSI | Up to 176 °F | NPT Threads

Insertion Thermal Air Flow Switch
KAL-L - Thermal Air Flow Switch

Temperature Compensated | Easy to Install | Adjustable Response Time | Up to 66 ft/sec | Up to 120 PSI | Up to 250 °F | NPT Thread or Flange | Suitable for HVAC

Industrial Thermal Mass Flow Meter
KEC - Thermal Energy Flow Meter

For Gases | No Moving Parts | Fast Response Time | Up to 100 bar | Up to 180 °C | NPT Threads or ANSI 150/300 Flanges


KOBOLD USA is a subsidiary of KOBOLD Messring GmbH, a world-leading instrumentation engineering business founded in Germany in 1980 by Klaus J. Kobold. With patented technology and superior service, the company quickly established itself as one of the global leaders in sensor and control systems with high quality products. The KOBOLD brand name became synonymous with superior quality and technological advancement in instrumentation engineering.

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